


Naughty Knotty

by dracoqueen22



Category: Transformers Generation One
Genre: Beast Mode Sex, Dinomode Sex, Domination, Grimlock in Dinomode, Grimlock knotting in Dino-mode, Grimlock's accent is hard, Knotting, M/M, Size Kink, Sticky Sexual Interfacing, alt mode sex
Language: English
Status: Completed
Published: 2015-07-23
Updated: 2015-07-23
Packaged: 2018-04-10 20:42:31
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,604
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/4406984
Author URL: https://archiveofourown.org/users/dracoqueen22/pseuds/dracoqueen22
Summary: <blockquote class="userstuff">
              <p>Optimus has a desire that Grimlock is all too happy to fill.</p>
            </blockquote>





	Naughty Knotty

**Author's Note:**

> For the Flash Fiction prompt of Grimlock/Optimus which I took and ran into this glorious piece of smut. *evil laughter*

Optimus panted as his hands scraped the berth. The squelch of four fingers pushing in and out of his valve was almost obscenely loud for all that his rumbling engine overshadowed it.   
  
“That's--that's good enough,” Optimus moaned. His knees trembled. “Do it.”   
  
Grimlock chuckled and removed his fingers, wiping them on Optimus' aft. “Me Grimlock decide when it's good enough,” he said.   
  
Optimus huffed. “Don't start playing games with me now.”   
  
Grimlock patted his aft again before Optimus heard the distinct sound of transformation. A wave of lust swept through Optimus' frame.   
  
He spread his pedes wider, eagerly anticipating the blunt push of a thick spike into his aching valve. His calipers clicked restlessly. Lubricant trickled down his thighs and dripped onto the floor.   
  
Optimus shivered. “Grimlock,” he demanded. “Do it.”   
  
He braced himself.   
  
Wet heat lapped at his swollen entrance. Optimus jerked, pleasure shooting through his array as much as surprise. He'd expected a spike, not the soft sweep of a glossa. Optimus gasped and rose onto the tips of his pedes, aft canting upward. Hot ventilations ghosted over his wet array, his valve fully exposed to the broad glossa flicking over his puffy folds and throbbing anterior node.   
  
Optimus groaned and buried his face in the berth cover. He heard the cotton give a distressed noise as his fingers gripped tighter. His valve clenched down on nothing and heat flooded his lines. As good as it felt, he wanted a spike in him. Grimlock was just being a fragging tease!  
  
Grimlock's glossa swept over his valve again and then his snout nosed between Optimus' legs. The top of it bumped up, pushing Optimus' hip upward and lifting him clear off the floor. He flailed, scrambling to adjust as Grimlock nosed him up onto the berth. His knees perched on the edge.   
  
“Better,” Grimlock said. He sounded smug. Then again, he always sounded smug. There wasn't a modest strut in the Dinobot leader's entire frame.   
  
Optimus flicked a glare over his shoulder, but it was hard to stay angry when Grimlock lapped at his anterior node again. His knees wobbled.   
  
“Do you enjoy dragging things out?” Optimus hissed.   
  
Grimlock snickered. Optimus heard the shift and hiss of hydraulics as Grimlock straightened, rising to his full height. He loomed over Optimus and the berth in dinomode; his helm barely cleared the ceiling of Optimus' quarters. Lubricant glistened on the end of his snout and Optimus resisted the urge to lick it off.   
  
“Me Grimlock no want to hear complaints later,” he said and if it was possible for a Tyrannosaurus to smirk, Grimlock was doing so now. His tail flicked around the room, knocking into a nightstand. “You Prime not as sturdy as Dinobot.”   
  
“I think you're stalling.”   
  
Grimlock outright laughed. He leaned forward, smaller hands grasping at Optimus' aft and groping him. Three taloned fingers slid into Optimus' valve, prodding all around before Grimlock pulled back.   
  
“Me Grimlock guess you primed enough,” he said, snickering at his own pun. “You Prime ready?” The click of a spike panel sliding aside carried to Optimus' audials.  
  
Optimus full-frame shivered and shoved his knees as far apart as was physically comfortable. “Yes.”  
  
He didn't have to look to know what was coming. He'd already spent time on his knees, orally worshiping Grimlock's spike. It was the perfect size, smooth on the underside and flared on the top with a little ridge that caught on the nodes of his valve ceiling. Optimus shivered from the memory.   
  
He felt the wide tip of it press against his aft and valve. They were still working on finding the perfect placement and angle. Optimus shifted his weight and reached down between his legs, guiding the spikehead to his valve. He moaned as the blunt tip breached his rim, pushing past his plump folds.   
  
Down went his arms, his elbows bracing into the berth. He ex-vented as Grimlock slid into him, slowly, always so slowly. Carefully, like no one believed him capable. His spike was thick and smooth, testing the stretch of Optimus' calipers. Optimus shook, more lubricant slicking his valve. Drizzles of pleasure set his array ablaze.   
  
Grimlock's spike grew wider at the base, wide enough for capacity warnings to rise in Optimus' processor. He dismissed them. There was no danger of damage. He'd done this before. He'd loved it before.   
  
The widest bit of Grimlock's spike nudged at Optimus' rim. His valve resisted, seeking to repel something that was just a tad too large.   
  
Optimus hissed a curse and his fingers scratched at the berth. He shoved his aft higher, pushed his chestplate down against the berth.   
  
Grimlock growled above him; his talons scraped the floor. Optimus braced his knees on the edge of the berth and pushed back just as Grimlock thrust forward. With a pop, Grimlock's spike slid home. The rim of Optimus' valve closed around Grimlock's spike, cycling down into a tight ring that locked him in place.   
  
Optimus trembled, pleasure streaking through his lines like lightning. He panted as his valve rippled, as charge flashed through his array in a small overload. Optimus rubbed his face against the berth and rocked back toward Grimlock. It did little to move the massive spike in his valve, only shifting the pressure on his inner nodes.   
  
“Me Grimlock think you Prime smaller,” Grimlock said, but smugness was gone, replaced by the edge of arousal.   
  
“Maybe you're just bigger,” Optimus panted.   
  
Grimlock chuckled and Optimus felt the wet swipe of a glossa across the back of his helm. “Me will be,” he said.   
  
Optimus could already feel it. As lust pulsed in Grimlock's field and his spike throbbed in Optimus' valve, it was swelling. The bulbous base was thickening in circumference, forming a knot that would keep him trapped in Optimus' valve until he overloaded.   
  
Given enough force, he could tear free. It had happened before, much to Optimus' agony, Ratchet's cursing, and Grimlock's genuine remorse. Pain had not been the intent. Neither had damage.   
  
But there had been a certain matter of imbalance and a knee slipped and Optimus lost his grip. He fell one way and a heavy Tyrannosaurus fell another way and with a crunching pop, pain replaced pleasure.   
  
That was gone from now. Optimus was firmly planted on the berth. Grimlock had him pinned against it, his pedes braced on the floor. No chance of slipping. No chance of damage. Grimlock had refused to touch Optimus again until they could be sure of it.   
  
Grimlock swelled within his valve a bit further, dragging Optimus back to the present. His calipers stretched wide, so open that they no longer twitched. Lubricant gathered in his valve, but had nowhere to go except to gather at the ceiling of his valve, increasing the pressure. Optimus panted as pleasure built up in him, a slow and steady climb upward.   
  
His valve throbbed. Sensor nodes sparking with charge as they ignited the receptors of Grimlock's spike. He felt every pulse and swell of Grimlock's spike. More tangible was the perception of _mass_ hanging over him.   
  
Grimlock had him pinned. Optimus couldn't move, couldn't escape unless he demanded that Grimlock back off. While Grimlock's hands weren't quite long enough to grab him and hold him down, his denta were nothing to dismiss.   
  
Optimus whimpered as he felt Grimlock's glossa flick over his shoulders and the scrape of Grimlock's denta rasp against his armor. Grimlock's hips shifted, but rather than shift his spike, all it did was tug on Optimus' pelvis. Grimlock's entire frame rumbled as his spike reached maximum swell and locked into place.   
  
Grimlock's rolling purr sent shivers down Optimus' spinal strut. “You Prime okay?”   
  
Optimus swallowed down an overabundance of oral lubricant. He rebooted his vocalizer as the first try produced nothing but a wave of static. His knees trembled. His exterior nub throbbed with impending overload.   
  
“Fine,” he bit out as his fingers twisted the berth cover. “For the love of Primus, keep going. I'm so close.” He gasped out another moan and shoved his face into the berth, trying to keep the noises to a minimum. His calipers trembled, rippling around Grimlock's spike in a desperate, but continuously aborted attempt to cycle down.   
  
“Not fair,” Grimlock growled. He rocked a thrust forward, shoving Optimus further up the berth, before he pulled back, dragging Optimus with him.   
  
Optimus gasped aloud, pleasure like a lightning bolt to the systems. He didn't know arousal could feel like this, molten and present and overwhelming. Grimlock could so easily overpower him, throw him around like a rag doll, push him down and frag the overloads out of him. Optimus' panel popped at the thought. His spike sprang free, dribbling prepatory transfluid onto the berth.   
  
Optimus shuddered. His valve rippled again. Overload peeked at him from around the corner. Static snapped through his systems.   
  
“Me Grimlock doing all the work,” Grimlock said with another impatient jerk of his hips.   
  
Optimus yelped as the thrust pushed Grimlock that last precious inch inside of Optimus. The thick swell of his spike head scraped over Optimus' ceiling node.   
  
Overload slammed through Optimus and he convulsed, valve clutching hungrily at Grimlock's spike. His vents dumped heat into the air. His cooling fans spun so quickly his entire frame vibrated.   
  
It wasn't enough.   
  
Optimus sagged and panted, knees pushing down on the berth as Grimlock's spike remained trapped in his valve. Charge continued to gather. Lubricant seeped into what little empty space was left in his valve, making him feel oh so full.   
  
“Such a g-good job, you're doing,” Optimus managed to gasp out. He braced himself against the berth with wobbling elbows.   
  
Grimlock leaned down, looming without trying. It changed the angle slightly and the tip of Grimlock's spike hit another deeply buried sensor. Optimus groaned and rocked his hips back, riding Grimlock's spike without shame. All his valve could do was ripple around it. Each squeeze of his calipers sent another shock of pleasure through his array.   
  
Above him, Grimlock growled. Every throb of his spike seemed in counterpoint to the squeeze of Optimus' valve.   
  
“You Prime small,” Grimlock grunted, but it came off as less a complaint and more a compliment.   
  
He rocked forward, tiny motions that rocked Optimus' frame on the berth. Every push ground Grimlock's spike head against Optimus' ceiling node. It wasn't long until he was panting again, meeting each of Grimlock's thrusts with a push of his own.   
  
Grimlock's concentration started to crumble. His own ventilations turned to heavy, rattling bursts. His cooling fans roared. His vocalizer spat tiny grunts and growls. His spike swelled again, and Optimus' valve protested. More warnings cropped up that he barely spared a moment to dismiss.   
  
It was very little motion, but so much friction. Optimus pressed his forehelm to the berth and looked down, seeing his spike bobbing between his legs. His untouched anterior node was swollen and desperate. He imagined, in the shadows, that his abdominal plating was bulging, that the outline of Grimlock's spike could be seen. He was full, valve beyond maximum capacity, and the single thought made Optimus moan even louder.   
  
He braced himself with one arm and reached down, wrapping his fingers around his spike. He stroked himself furiously, thumb squeezing the tip of his spike to prolong the pleasure. He knew Grimlock was getting close and Optimus' own overload threatened to peak again. Each thick grind of Grimlock's spike against his ceiling node sent a ripple of pleasure through his valve.   
  
“C-close,” Optimus warned, though it was pretty obvious.   
  
Grimlock snorted. “You Prime have no stamina.”   
  
“Shut up.”   
  
“Dinobot stronger,” Grimlock added with another laugh that trailed into a low moan as he rocked harder into Optimus.   
  
Optimus grunted, valve cycling down as he squeezed his spike. He tried to rebut Grimlock's challenge but all that came out was a growled, “ _Harder.”_  
  
Grimlock shoved him across the berth and yanked him back, again and again. Optimus felt out of control and desperate and he loved it. Grimlock ex-vented searing heat down on Optimus' back. His aft rubbed against Grimlock's ventrum in a scrape-scrape of metal on metal.   
  
Pleasure built and built. Optimus' awareness narrowed down to his hand furiously working his spike and Grimlock's mass shifting inside of his valve. He sounded as bestial as Grimlock, snarling as he fought for another overload, until the bubble burst within him.   
  
Optimus gasped, backstrut bowing hard as overload swamped through him. His valve clenched down, nearly to the point of pain, his entire frame drawing taut. His processor flashed, vision gone white, as charge crashed over him.   
  
Grimlock roared, bowing upright as he finally overloaded. Optimus felt the first hot spurt wash over his internal nodes. It fought for space with the lubricant already filling his valve. The added pressure felt like someone was grinding against his ceiling node and Optimus overloaded again, gasping for cooler air as each subsequent spurt of Grimlock's spike sent a shock of pleasure through his system.   
  
It seemed to go into forever. Optimus buried his face in the berth, one hand gripping the cover so tightly that his fingers ached. He shook and shook as his sensory net exploded with heat and ecstasy.   
  
Grimlock's growls echoed in his audial. He bucked his hips and another hot spurt of transfluid freed him from Optimus' valve. Optimus slid forward, collapsing on his belly on the berth as another wet spurt striped his aft and back. A sloppy mix of fluids streamed from his valve. He heard it patter to the floor. He then heard the unmistakable sound of transformation as Grimlock abruptly reverted to root mode and stumbled backward.   
  
Warmth suffused his frame, left him feeling weak. Optimus sighed as he flopped completely on the berth, draped over the side with his lower half hanging off. His valve was still open and leaking fluids down his thighs. His cooling fans whirred, the temperature in the room too hot for comfort.   
  
It took effort, but he managed to turn over to his back, thighs still obscenely splayed. Grimlock was leaning against Optimus' deck, his hips and thighs splattered with lubricant and transfluid. His spike had retracted, but the panel remained open, giving Optimus a peek of the generous equipment within it.   
  
Optimus licked his lips. A little bit of oral treatment and he was sure he could coax it out again, perhaps for another round.   
  
“You Prime satisfied?” Grimlock asked. It was probably an attempt to sound smug, but given the sated hum to Grimlock's field, it didn't quite work.   
  
Optimus revved his engine. “Always.”   
  
He noticed, however, that Grimlock's gaze was drifting to his bared valve. Optimus made a point to reach down, dragging his fingers through the sticky mess between his legs. He shivered as he brushed over his anterior nub, igniting a spark of heat.   
  
“There's a mess though,” he said, holding Grimlock's gaze as his visor shifted toward Optimus. “Might need to take care of it.”   
  
“Now you Prime teasing,” Grimlock said but he lurched forward anyway, notching himself between Optimus' thighs and planting his hands on the berth to either side of Optimus' frame.   
  
Optimus hooked a leg around Grimlock and rolled his hips up. “It's only teasing if I don't follow through,” he purred. He licked his lips again.   
  
Back then, it had started with Optimus dropping to his knees and worshiping Grimlock's spike. It just didn't feel over until he got a chance to do it again.   
  
Grimlock leaned over him, rolling their interface arrays together. “Your move,” he said. His visor gleamed with challenge.   
  
Optimus smirked. “Make me.”   
  


****


End file.
